A filter device of this type is disclosed in EP 2 207 609 B1. In the known apparatus, conically shaped filter elements are provided, in particular in the form of slotted screen pipe elements. Due to the conical design, the spacing between the individual slotted screen pipe elements is increased in regions, as a result of which the volute in the filter housing is also enlarged. In the case of backwashing, the conical filter element has a clear advantage over a cylindrical filter element. One reason for this advantage is the relatively larger outlet cross section of the filter elements at the lower end, as compared to cylindrical filter elements having the same filter surface, because the larger outlet cross-section at the lower end facilitates the discharge of contamination with the backwash fluid. The pressure control element of the pressure control mechanism controls a flow of unfiltrate to the backwashing filter element to support the backwash and is allocated to the upper, open end of the relevant filter element. Due to the conical filter element shape, the upper open end has a smaller opening cross section.
Accordingly, in the known apparatus, the filter inlet for the supply of the unfiltrate is located above the filter elements. During filtration, the unfiltrate flows into the filter cavities by the openings that have the smaller opening cross section, which flow is not optimal in terms of flow resistance.